Male B6C3F1 mice given lindane daily at doses of 20 and 40 mg/kg body weight by gavage In corn oil for 3 days had suppressed bone marrow cellularity. erythrocyte precursors (CFU-E). granulocyte-macrophage progenitor cells (CfU-GM). and residual progenitor cell damage. which could be demonstrated by two whole body irradiations (WBI) at 200 rads. Lindane exposure for 10 consecutive days at doses of O. 10. or 20 mg/kg did not cause clinical abnormality or changes in body weights. but there was a dose-dependent decrease in marrow cellularity. in more pluripotent stem cells (CFU-S). and in committed CFU-GMs which returned to control values by four weeks. These mice were then subjected to two 100-rad exposures of WBI at four and nine weeks following cessation of lindane treatment. This level of irradiation caused only a transient drop in marrow progenitor numbers. Control and lindane-exposed mice were examined at one and six weeks following the last irradiation, which was 10 and 15 weeks following the final lindane exposure. the lindane- exposed mice had lower progenitor cell numbers and slower recovery from the irradiation. These results indicate that lindane has significant myelotoxicity in mice and short-term lindane exposure can induce residual progenitor cell damage that can be demonstrated by subsequent irradiation.